The present invention relates, in general, to a device and method for inducing controlled cracks in concrete to avoid unsightly cracks on the outer surface of concrete structures.
When concrete shrinks during the hydration period, stress in the concrete is relieved by cracking. The cracking is addressed in many ways depending on the conditions or use. In most structural concrete, cracking is expected and is not a problem unless the surface is subject to water intrusion, is exposed to view, or both. Then, the issue of cracking becomes paramount.
An important characteristic of architectural concrete, which is the high end of exposed concrete work, is that it have pleasing visual surfaces. When a surface is marred by unsightly cracking, or cracking which is leaching white salts, it becomes displeasing and ugly.
Cracking can be reduced through attention to the design of temperature reinforcement, optimum mix, and high quality placement and curing procedures. A wall of the same profile throughout, will crack every 10 to 16 feet or so.
In addition, cracks may appear due to isolated restraint or weakening of the wall. Restraint due to additional reinforcement, such as in-the-wall column reinforcing or intersecting wall bars, or whether the volume of the wall is reduced by openings or offsets in thickness, may also cause cracks.
There are very specific and positive ways of planning and executing concrete work relating to crack control. since cracking is a natural part of a concrete surface, it is desirable to control it so that the cracks occur in a location where they are acceptable to the appearance and also so that they can be sealed against moisture.
Unfortunately, the method most often used to address cracks in both design and construction is to ignore them. Since cracking is inevitable, it is easy to dismiss the issue and hope that the cracking will not deter from the appearance or allow moisture to enter the structure.
Ignoring cracking in exposed concrete work may suffice for a time. However, cracks will start to show. The inevitable signs of streaking where weather darkens the cracks, where white salts are brought to the surface or by leakage when water penetrates into the interior of a building, soon appear.
Allowing cracking to appear without any control is only effective when the concrete surface is heavily textured and is not exposed to weather. In this case, the texture is such a dominant feature that the cracks do not detract from the appearance and, of course, there is no water to affect the surface.